Modeling of seismic attenuation in fracture-filling gas hydrate-bearing sediments and its application to field observations in the Krishna-Godavari Offshore Basin, India

Abstract

Understanding the attenuation mechanism in gas hydrate-bearing sediments (GHBS) is essential for accurate quantification of natural gas hydrates, yet previous rock physics models fail to explain the observed attenuation suppression at seismic frequencies when hydrates occur as fracture-filling morphology. Here we present a new model to decipher the viscoelastic performance of fracture-filling GHBS, by treating it as a composite of host sediment and pure gas hydrate. We first characterize the attenuation in the host sediment without hydrate by the viscous fluid flow in swelling clay minerals. Then, based on laboratory data, we quantify the mechanical performance of pure gas hydrate, exhibiting that hydrate is a consolidated aggregate with properties different from unconsolidated host sediment. After incorporating fracture-filling gas hydrates into the host sediment, the properties of host sediment are significantly modified and the resulting model reproduces the suppressed attenuation observed in field. We apply this model to the field attenuation extracted from multichannel seismic data in the Krishna-Godavari Offshore Basin in India, where gas hydrate was found filled in fractures. The results show that the attenuation and hydrate concentration predicted by our model agree well with the field measurements, which suggests the promise of our model in detection and quantification of nature gas hydrates in clay-dominated sediments using seismic data.